I did almost all of the soft panels in my Camaro and I used SEM's Vinyl paint. I also read up on it a lot and I am VERY pleased with the results on my parts. I cleaned everything up really well multiple times with soap and water. Then I cleaned it all with PREPSALL, and I think what is the most important part wiped it all down with lacquer thinner and let it dry. Then I sprayed a couple light coats, followed by one heavy coat at the end. I only did a pair of parts at a time so I had a good working window, but once dry I can scratch my nail across it and it doesn't peal up or anything.
As for the hard plastics, I got lucky and mine were already black.